The QuEChERS Approach for the Determination of Pesticide Residues in Soil Samples: An Overview.

Soil samples are complex matrixes; therefore, soil sample preparation is a critical step, and one that is usually expensive, time-consuming, and labor intensive. The quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, originally developed for the determination of pesticides in fruits and vegetables, has been recently modified and adopted for the analysis of pesticides in soil. This paper reviews all aspects of sample preparation, including extraction and clean-up, and describes the applications of conventional and modified QuEChERS techniques. It also presents a comparison of the QuEChERS method with other methods used for sample preparation for determination of pesticides in soil.

The QuEChERS Approach for the Determination of Pesticide Residues in Soil Samples: An Overview.

Soil samples are complex matrixes; therefore, soil sample preparation is a critical step, and one that is usually expensive, time-consuming, and labor intensive. The quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, originally developed for the determination of pesticides in fruits and vegetables, has been recently modified and adopted for the analysis of pesticides in soil. This paper reviews all aspects of sample preparation, including extraction and clean-up, and describes the applications of conventional and modified QuEChERS techniques. It also presents a comparison of the QuEChERS method with other methods used for sample preparation for determination of pesticides in soil.

Rhythmic U2af26 alternative splicing controls PERIOD1 stability and the circadian clock in mice.

The circadian clock drives daily rhythms in gene expression to control metabolism, behavior, and physiology; while the underlying transcriptional feedback loops are well defined, the impact of alternative splicing on circadian biology remains poorly understood. Here we describe a robust circadian and light-inducible splicing switch that changes the reading frame of the mouse mRNA encoding U2-auxiliary-factor 26 (U2AF26). This results in translation far into the 3' UTR, generating a C terminus with homology to the Drosophila clock regulator TIMELESS. This new U2AF26 variant destabilizes PERIOD1 protein, and U2AF26-deficient mice show nearly arrhythmic PERIOD1 protein levels and broad defects in circadian mRNA expression in peripheral clocks. At the behavioral level, these mice display increased phase advance adaptation following experimental jet lag. These data suggest light-induced U2af26 alternative splicing to be a buffering mechanism that limits PERIOD1 induction, thus stabilizing the circadian clock against abnormal changes in light:dark conditions.

Activation-induced tumor necrosis factor receptor-associated factor 3 (Traf3) alternative splicing controls the noncanonical nuclear factor κB pathway and chemokine expression in human T cells.

The noncanonical nuclear factor κB (ncNFκB) pathway regulates the expression of chemokines required for secondary lymphoid organ formation and thus plays a pivotal role in adaptive immunity. Whereas ncNFκB signaling has been well described in stromal cells and B cells, its role and regulation in T cells remain largely unexplored. ncNFκB activity critically depends on the upstream NFκB-inducing kinase (NIK). NIK expression is negatively regulated by the full-length isoform of TNF receptor-associated factor 3 (Traf3) as formation of a NIK-Traf3-Traf2 complex targets NIK for degradation. Here we show that T cell-specific and activation-dependent alternative splicing generates a Traf3 isoform lacking exon 8 (Traf3DE8) that, in contrast to the full-length protein, activates ncNFκB signaling. Traf3DE8 disrupts the NIK-Traf3-Traf2 complex and allows accumulation of NIK to initiate ncNFκB signaling in activated T cells. ncNFκB activity results in expression of several chemokines, among them B cell chemoattractant (CxCL13), both in a model T cell line and in primary human CD4(+) T cells. Because CxCL13 plays an important role in B cell migration and activation, our data suggest an involvement and provide a mechanistic basis for Traf3 alternative splicing and ncNFκB activation in contributing to T cell-dependent adaptive immunity.

Prediction of extraction efficiency in supported liquid membrane with a stagnant acceptor phase by means of artificial neural network.

An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol-water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back-propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol-water partition coefficients logP, acid dissociation constant pK(a), water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters.

Separation of benzyl derivatives of germanium for HPLC.

The paper presents interactions of mono-, di-, tri-, and tetrabenzyl derivatives of germanium with stationary phase surface and results from these processes of determination. As a final result of the work, optimal conditions of chromatographic separation and determination of these compounds by high-performance liquid chromatography (HPLC) method are proposed. During investigations, different types of stationary phase (including octadecyl, octyl, and chemically bonded aryl phases) and mobile phases are considered. As a result of the investigation, the highest selectivity is showed chemically by bonded aryl stationary phase combined with a mobile phase consisting of acetonitrile (capacity factors of di-, tri-, and tetrabenzyl derivatives of germanium k(1) = 0.86, k(2) = 2.53, k(3) = 6.45). However, octadecyl phase, which is considered as reference phase, exhibits the lowest separation factors of determined benzylgermanium compounds (k(1) = 9.12, k(2) = 37.62, k(3) = 70.43).

Quantitative structure-retention relationship studies as an analytical tool in the determination and modeling of pesticide residues in plant organisms.

Crop models use mathematical equations to simulate the physical and chemical processes that generally control the uptake, translocation, and sorption of pesticides in all parts of plants. Our interest is focused on method optimization to determine the new compounds using stationary and mobile phases with different physicochemical properties. The work deals with five fungicides composed of nitrogen-containing heterocycles, 1,2,4-triazoles. The sample preparation liquid extraction and solid-phase-based methods are used to determine and model the pesticide residues in plants organisms. Analysis of these compounds is generally carried out by GC or HPLC coupled to different detectors, especially to mass spectrometers, in hyphenated techniques that have been extremely developed in recent years. The relationships between the chromatographic retention factor (k) and those physicochemical properties that are relevant in quantitative structure-retention relationship (QSRR) studies were investigated. The accuracy of the simple linear regressions between the chromatographic retention and the descriptors for all of the compounds was satisfactory (correlation coefficient 0.83 < or = R2 < or = 0.99). The QSRR models of these nitrogen-containing heterocyclic compounds could be predicted with a multiple linear regression equation having the statistical index R2 = 1.00. Evaluation of chromatographic properties of the new stationary phases and description of the molecular separation mechanism using the QSRR method, including molecular modeling, were performed. A universal model is presented that links the physicochemical parameters describing the fungicide compounds with the anatomical, physiological, and biochemical properties of the plant.

Influence of temperature on mass transfer in an incomplete trapping supported liquid membrane extraction of triazole fungicides.

The influence of temperature in a supported liquid membrane (SLM) extraction of triazole fungicides was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperatures ranging from 5 to 40 degrees C. Increase in temperature led to an increase in diffusion coefficient and flux with a flowing acceptor solution. The apparent viscosity also decreased with an increase in temperature. However, the increase in mass transfer parameters did not result in an overall increase in extraction efficiency with a stagnant or circulation acceptor phase. Stripping of the analytes from the membrane into the acceptor phase as well as the configuration of the extraction unit could have limited the influence of temperature on mass transfer. The partition coefficient of analytes from the acceptor solution to the membrane, K(A), was found to be much higher than that from the donor solution to the membrane K(D), thus triazole compounds preferred to remain in the membrane even with an increased extraction temperature.

High performance liquid chromatography of 1,1-diamino-2,2-dinitroethene and some intermediate products of its synthesis.

1,1-Diamino-2,2-dinitroethene (DADNE, FOX-7) is a novel explosive with low sensitivity and high performance. The unique combination of the valuable properties is a result of the structure of the compound. The molecular packing of DADNE consists of layers with strong intermolecular hydrogen bonds which stabilize the molecule. In the paper, the results of research the purity of DADNE in different recrystallization conditions and some intermediate products of its synthesis were presented. High performance liquid chromatography (HPLC) method based on the porous graphitic carbon (PGC) column packing material has been developed. Two variants of mobile phases in different pH values: acetonitrile-water and methanol-water with ammonia (NH(3)) and with trifluoroacetic acid (TFA) were used. The probable mechanism of interaction between the analyte, the stationary phase, and the mobile phase was suggested.

Influence of temperature on mass transfer in an incomplete trapping single hollow fibre supported liquid membrane extraction of triazole fungicides.

The influence of temperature in a single hollow fibre supported liquid membrane extraction of triazole fungicides with a stagnant acceptor phase was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperature ranging from 278 K to 313 K. Increase in temperature led to an increase in diffusion coefficient and flux. The apparent viscosity also decreased with an increase in temperature. The degree of trapping in the acceptor phase influenced the mass transfer at higher temperature. At lower temperature, the transport of analytes from the donor solution through the donor-membrane interface and through the membrane mainly affected the transport of triazole fungicides. The effect of temperature in a single hollow fibre SLM extraction technique is therefore more pronounced where transport is donor controlled and/or membrane controlled. The partition coefficient of analytes from the acceptor solution to the membrane, K(A) was found to be much higher than that of from the donor solution to the membrane K(D), thus least trapped triazole fungicides preferred to remain in the membrane even with an increased extraction temperature.

Comparative evaluation of high-performance liquid chromatography stationary phases used for the separation of peptides in terms of quantitative structure-retention relationships.

Chromatographic measurements were made on 17 physicochemically diversified high-performance liquid chromatography (HPLC) columns which were further analyzed in terms of their similarities and dissimilarities for 25 carefully designed, structurally diverse peptides showing distinctly distinguished groups. The goal of the study was to investigate the molecular mechanism of retention and to find an objective manner of quantitative comparison of retention properties and classification of modern stationary phases for reverse phase HPLC (RP-HPLC). We utilized the structural descriptors of peptides obtained from molecular modeling to describe their chromatographic retention behavior under given HPLC conditions. Quantitative structure-retention relationships (QSRR) with the following descriptors were employed: logarithm of the sum of amino acid retention contributions in a given peptide, logSumAA, logarithm of the Van der Waals volume of the peptide, logVDWvol, and logarithm of its calculated n-octanol/water coefficient, clogP. The best QSRR equations were obtained in the case of monolithic and regular octadecylsilica columns. On the other hand, the combination of QSRR and principal component analysis (PCA) can be considered as the efficient tool allowing column classification and searching for orthogonal HPLC conditions required to separate peptides.

HPLC columns partition by chemometric methods based on peptides retention.

In recent years, multivariate techniques have been utilized to evaluate reversed-phase high-performance liquid chromatographic data. In the present study, 11 high-performance liquid chromatography (HPLC) columns were divided into several groups according to the retention factors of 12 peptides. Principal component analysis (PCA) and cluster analysis (CA) were used in column and peptides' comparison and grouping. CA results indicated that all stationary phases may be generally grouped into several clusters, due to stationary phase structure and properties. On the other hand, interesting results were obtained with the use of PC. There is almost linear relationship between classified HPLC columns in the space of new PCs, which is connected with meaning of the PC's reflected in their loading values. The first component describes non-polar properties of peptides, whereas the second component is loaded with polar peptides having much lower logP values. PCA and CA were also used in peptides comparison however, complete explanation of peptides grouping still remains unclear.

Evaluation of reversed phase columns designed for polar compounds and porous graphitic carbon in "trapping" and separating neurotransmitters.

Quantification of neurotransmitters as biologically active analytes in neurological samples is of high interest for studying their effect on multiple targets. This work is part of a strategy involving two-dimensional liquid chromatography (2D LC) system with mass spectrometry (MS) detection. The concept of the on-line LC system is the coupling of reversed phase liquid chromatography (RPLC, the second separation dimension) to ion-exchange chromatography (IEC, the first dimension). Our objective in this study is to find the appropriate second dimension column, ensuring that samples of neurotransmitters are refocused and separated on it. Silica-based columns designed specifically to retain polar compounds were tested in LC conditions and compared with results obtained with a porous graphitic carbon (PGC, Hypercarb) column. These polar embedded, polar endcapped, and high-density alkyl chain columns successfully separated analytes in question using mobile phase systems with high percentage of water, or even pure water. Only Hypercarb column provided efficient retention of the most polar neurotransmitters and could be used for trapping and preconcentrating the compounds without rapid breakthrough.

Optimization of a matrix solid-phase dispersion method for the determination analysis of carbendazim residue in plant material.

The objective of this paper was to prove that matrix solid-phase dispersion (MSPD) coupled with high performance liquid chromatography (HPLC) and column switching could be used for the determination and quantification of carbendazim residue in plant samples. By comparing results obtained after optimization of the extraction conditions on an acidic silica gel column, it was determined that sorption and retention of carbendazim were achieved via specific interactions. The method of standard additions was used for quantitative analysis. Its performance was evaluated and validated: the detection limit (UV-Vis detection at lambda=279 nm) was 0.02 microg/g, the relative standard deviations (R.S.D.) were between 2.7 and 4.1% and the recoveries were ranging from 84.3 to 90.7% at the 0.04, 0.08 and 0.1 microg/g fortification levels. The method was successfully tested on cereal samples, and the results obtained with the present off-line MSPD-HPLC procedure were found to compare well with those obtained with procedure involving LLE.